Use of silicone compositions crosslinkable by the cationic route under UV radiation and of a photoinitiator of the onium borate type for coatings for sheet gaskets, in particular cylinder head gaskets

ABSTRACT

The invention concerns the use of cross-linkable silicone compositions for fast, economical and simple impregnation and/or varnishing of flat joints (e.g. cylinder head gaskets). More precisely it concerns the use of silicone compositions cross-linkable under UV radiation, by cationic process and in the presence of specific phoinitiators selected among onium borates or organometallic complexes, of which the borate counter-anions contain at least a boron bound to at least a substituted phenyl (Me, F). The silicone liquid precursor is a polydimethylsiloxane (PDMS) substituted by cross-linking functional groups, by cationic process (G f     p   ) under UV of the epoxy or vinyloxy type. These G f     p    are present at the rate of 0.15 to 2.0 pr kg of PDMS. The invention also relates to the method for impregnating/varnishing flat joints (e.g. cylinder head gaskets) using the specific PDMS composition+photoinitiator of borate type as well as the treated joints and the composition themselves.

[0001] The area of the present invention is that of siliconecompositions based on organofunctional polyorganosiloxanes (POS)crosslinkable by the cationic route under the effect of activationobtained via light radiation, preferably UV radiation, and/or via anelectron beam and/or via thermal energy.

[0002] More specifically, the invention relates to the use of suchcompositions for the treatment of sheet gaskets, in particular forimpregnating or varnishing cylinder head gaskets of internal combustionengines.

[0003] It relates in particular, using these compositions crosslinkableby the cationic route under UV radiation, e.g., to impregnating sheetgaskets (cylinder head gaskets) and/or to preparing antiadhesivecoatings at the engine block/cylinder head interface of heat engines,the said interface preferably being the cylinder head gasket itself.

[0004] The silicone compositions used for this purpose were not untilnow silicone compositions crosslinkable by the cationic route under UVradiation.

[0005] The functioning of an internal combustion engine requires strongcohesion of the stationary components, thorough lubrication of themoving components and efficient cooling of the engine block assembly.The cylinder head gasket has a two-fold role; it provides for thecohesion of the engine block/cylinder head dismountable assembly and forthe leaktightness of the intersecting circulations of the cooling liquid(water to which glycol and alkaline agents have been added), oil andgases in the course of combustion.

[0006] Cylinder head gaskets can be made of highly complex compositematerials comprising a metal core made of finely perforated sheet metal,a board (preferably devoid of asbestos) composed of organic fibres andof inorganic fillers, crimped firing rings opening on the explosionchamber, and a curb made of silicone elastomer to contain possible leaksonto the surface.

[0007] Cylinder head gaskets can also be composed simply of one or moremetal sheets optionally covered with an NBR rubber elastomer coating orfluorinated elastomer coating of the Viton type (cf., for example,JP-A-082 09 113).

[0008] Cylinder head gaskets are generally subjected, prior to theiruse, to two types of treatment using silicones:

[0009] 1—an impregnation treatment intended to fill the voids in orderto render the board water-repellent and to improve its thermalbehaviour,

[0010] 2—and a varnishing treatment intended to lower the coefficient offriction of the gasket and to bring about good antiadhesiveness.

[0011] In addition to these treatments, a curb made of siliconeelastomer is also deposited, by silk-screen printing, on cylinder headgaskets.

[0012] The impregnation of cylinder head gaskets with crosslinkedsilicones is recommended in the case where the support is porous. Thismakes it possible to ensure leaktightness with regard to the variousoperating fluids of the engine (oils, petrol, fuel oil, cooling liquidor combustion gases). Furthermore, the impregnation provides the gasketwith a degree of compressibility which it has to have during theflattening to which it is subjected when the cylinder head is tightened.

[0013] When the cylinder head is taken off, the gasket must be removedvery easily without adhering to the surfaces of the cylinder head. It istherefore essential for both faces of the gasket to be antiadhesive andthis is one of the essential roles of the varnishing by crosslinkedsilicone compositions. Varnishing with the silicone contributes torendering leakproof but also to protecting the gasket with respect topossible damage during the operation of the engine (mechanical stress:thermal stress and/or shearing: heating/cooling).

[0014] The impregnating agents and varnishes conventionally used arecompositions composed of silicone oils or resins of low viscositycomprising SiOH or SiR functional groups (U.S. Pat. No. 4,720,316;EP-A-272,382) or Sivinyl functional groups (DE-A-3,731,032; U.S. Pat.No. 4,499,135) or of mixtures of a silicone oil or resin comprising SiHfunctional groups and of a silicone oil or resin comprising Sivinylfunctional groups (DE-A-3,718,559; EP-A-471,979; DE-A-3,544,740) capableof crosslinking at high temperature (generally greater than 100° C.) inthe presence of a metal catalyst, such as tin, titanium, zirconium orplatinum salts, or of a peroxide.

[0015] Compositions based on silicone oils or resins comprising SiOH,SiH, SiVinyl or SiH/SiVinyl functional groups generally exhibit at leastone of the following disadvantages:

[0016] the mixture composed of the silicone matrix and the catalyst isunstable at ambient temperature (in particular in the absence ofsolvent), this instability being reflected by an increase in viscosity,indeed even by a gelling, of the impregnation or . varnishing bath,which requires frequent replacement of the impregnation or varnishingbath or treatment in two stages; for example, Patents U.S. Pat. No.4,720,316 and EP-A-272,382 recommend the use of the catalyst during themanufacture of the board and then impregnation of the dried board with asilicone oil possessing SiH groups;

[0017] it is often necessary to disperse the silicone+catalyst mixturein an organic solvent in order to increase the stability and to decreasethe viscosity of the said mixture; this results in the disadvantagesrelated to the use of solvents (toxicity, provision of safety devices,of devices for recycling the solvent, and the like)

[0018] the cost price of the starting materials is high, in particularin the case of vinylated oils or resins optionally used in combinationwith oils or resins possessing SiH functional groups and with a platinumcatalyst; these mixtures can be very stable at ambient temperature, inparticular in the presence of a platinum inhibitor, but are expensivebecause of the use of vinylated oils or resins.

[0019] In the quest for a novel silicone composition for the treatmentof cylinder head gaskets having the object of improving theabovementioned known compositions (Rhône-Poulenc French patentapplication on cylinder head gaskets—No. 2,697,532), provision has beenmade to use a silicone composition crosslinkable by hydrosilylationcomprising an α,ω-diOH POS, a POS possessing an SiH unit of the PMHStype, and ethynylcycolohexanol, the latter compound making it possibleto form resins possessing a silanol functional group; the ratio of SiHto SiOH of the POS concerned being of the order of 10/1 to 30/1 and thecomposition also comprising a polyaddition catalyst of the Karstedttype.

[0020] Even if such a composition effectively leads to improvements withregard to stability, reactivity and flexibility of use, it still remainsthe case that the crosslinking specific to this type of compositioncomprises a restrictive stage of heating at high temperature (160° C.)for 5 to 10 minutes. Such a stage is particularly penalizing with regardto the productivity of an industrial process for the treatment orcoating of cylinder head gaskets using silicones. It may thus benecessary, for example, to resort to the use of sophisticated andexpensive equipment, such as long heating tunnels. It therefore seemsthat these silicone compositions, crosslinkable by polyaddition and usedfor the coating of cylinder head gaskets, still do not contribute anentirely satisfactory solution to the problem of carrying out siliconeimpregnation and treatment of cylinder head gaskets which meet thespecifications of antiadhesiveness and of compressibility, as well asthe requirements of productivity and of profitability for large scaleproduction.

[0021] French Patent Application No. 2,722,203 relates to theapplication of a crosslinkable fluorosilicone coating to a cylinder headgasket. Such a coating is obtained from a silicone compositioncrosslinkable, under the effect of heat, of UV radiation or of anelectron beam, by hydrosilylation. This composition comprises avinylated fluorosilicone, a POS carrying SiH units, a platinumhydrosilylation catalyst, a condensation catalyst of the peroxide typeand, optionally, a solvent of the halogenated solvent, aester or acetonetype. The support to which this composition can be applied is describedas preferably having a silicone nature. This coating is morespecifically intended to reduce the impermeability with respect to oilof cylinder head gaskets. It is a relatively thick coating: 0.1-10 mm,which is characterized by a relatively long crosslinking time of severalminutes and which has to be activated by heat for the crosslinking, evenin the cases where UV radiation is used. This known coating is thereforenot itself satisfactory either as regards the requirements related tolarge scale industrial production. Furthermore, the fact that thecrosslinking of this fluorosilicone composition is based on an SiH/SiVihydrosilylation mechanism poses problems of stability.

[0022] U.S. Pat. No. 5,260,348 also discloses a silicone compositioncrosslinkable under UV radiation according to a condensation mechanism.Such a composition is of use in the preparation of an antiadheseioncoating (release coating), in particular for cylinder head gaskets. Thiscomposition comprises an α,ω-diOH POS of the polydimethylsiloxane orpolydifluoroalkylsiloxane type, a crosslinking agent of the methyl- orethyltriacetoxysilane or methyltribenzoxysilane type, and aphotoinitiator formed by an onium (iodonium) salt, the counteranion ofwhich is BF₄ ⁻ or SbF₆ ⁻. These silicone compositions crosslinkableunder UV radiation by condensation have to be subjected to an additionalthermal activation in order to obtain reasonable crosslinking times. Itis obvious that this complicates the industrial process.

[0023] The counteranion with the best performance for crosslinking underUV radiation is SbF₆ ⁻ but it is found that it exhibits the majordisadvantage of being toxic.

[0024] It is therefore necessary to observe that, in the current stateof the art, there does not exist a crosslinkable silicone compositionentirely well suited to the requirements of the specific application,such as impregnation and/or coating of sheet gaskets and in particularcylinder head gaskets. The expected specifications for the impregnationand the varnishing of cylinder head gaskets, which are in particular theability to render leaktight, the compressibility, the antiadhesiveness,the stability and the ease of use and of preparation, are not satisfiedby the crosslinkable silicone compositions known to date.

[0025] In this state of knowledge, one of the essential objects of thepresent invention is to reveal a crosslinkable silicone composition forthe impregnation and the varnishing of sheet gaskets, in particular ofcylinder head gaskets, which overcomes the deficiencies of the prior artand in particular which offer a process for the application and for thepreparation/crosslinking of the silicone coating which is fast, whichdoes not require sophisticated equipment or high temperatures, and whichmakes it possible to obtain a sufficiently antiadhesive varnishingcoating possessing suitable mechanical properties.

[0026] Another essential object of the present invention is to find acrosslinkable silicone composition for the impregnation and/or thevarnishing of sheet gaskets, in particular of cylinder head gaskets,which is stable on storage, which is economical and which does notinvolve toxic solvents.

[0027] Another object of the present invention is to provide a processfor the coating of a sheet gasket, in particular of a cylinder headgasket, by impregnation and/or varnishing using a crosslinkable siliconecomposition, this process having to be easy to employ, to be economicaland fast, and to result in a silicone-comprising cylinder head gasketwhich is antiadhesive and which performs well in the surroundings inwhich it is used.

[0028] Another essential object of the present invention is to provide asheet gasket and in particular a cylinder head gasket coated and/orimpregnated with an antiadhesive and compressible crosslinked siliconeexhibiting all the expected specifications set out above as regards“processibility” and intrinsic qualities of the material.

[0029] Once these objects have been set, it is to the credit of theApplicant Company to have found, after many studies and experiments,that, entirely surprisingly and unexpectedly, it is appropriate toselect silicone compositions crosslinkable by the cationic route,preferably under activation by UV radiation, in which the initiator isan onium borate and/or a borate of organometallic cations having thedistinguishing feature of having a borate counteranion of an entirelyspecific nature, in particular in that it comprises a borate atom bondedto at least one phenyl radical substituted by at least oneelectron-withdrawing group. In addition to this advantageous selectionof the initiator, the Applicant Company has isolated a class of POScarrying organofunctional bridging groups (G_(f) _(p) ) crosslinkable bythe cationic route, for example of epoxide or vinyl ether type, in whichcompounds these G_(f) _(p) groups are present in an amount of at least0.01 equivalent per kg of POS.

[0030] Thus it is that the present invention relates to the use:

[0031] for carrying out impregnation(s) and/or for preparing, coating(s)which is (are) antiadhesive employed at the engine block/cylinder headinterface of engines and applied to sheet gaskets, in particularcylinder head gaskets,

[0032] of compositions based on at least one polyorganosiloxane (POS)crosslinkable by the cationic route, preferably under UV radiation, andon an effective catalytic amount of at least one initiator salt (PI),

[0033] the said use being characterized in that:

[0034] (i) the initiator salt (PI) is formed by at least one borate ofan onium of an element from Groups 15 to 17 of the PeriodicClassification [Chem. & Eng. News, Vol. 63, No. 5, 26 of Feb. 4, 1985]or of an organometallic complex of an element from Groups 4 to 10 of thePeriodic Classification (same reference),

[0035] □ the cationic entity of the said borate being chosen from:

[0036] 1)—onium cations of the formula (I):

[(R¹)_(n)−A−(R²)_(m)]⁺  (I)

[0037] in which formula:

[0038] A represents an element from Groups 15 to 17, such as, forexample, I, S, Se, P or N,

[0039] R¹ represents a C₆-C₂₀ carbocyclic or heterocyclic aryl radical,it being possible for the said heterocyclic radical to comprise nitrogenor sulphur as heteroelements,

[0040] R² represents R¹ or a linear or branched C₁-C₃₀ alkyl or alkenylradical; the said R¹ and R² radicals optionally being substituted by aC₁-C₂₅ alkoxy, C₁-C₂₅ alkyl, nitro, chloro, bromo, cyano, carboxy, esteror mercapto group,

[0041] n is an integer ranging from 1 to v+1, v being the valency of theelement a,

[0042] m is an integer ranging from 0 to v−1, with n+m=v+1,

[0043] 2)-the oxoisothiochromanium cations disclosed in PatentApplication WO 90/11303, in particular the sulphonium cation of2-ethyl-4-oxoisothiochromanium or of 2-dodecyl-4-oxoisothiochromanium;

[0044] 3) - sulphonium cations where the cationic entity comprises:

[0045] 3.1. at least one polysulphonium species of formula III.1

[0046] in which:

[0047] the Ar¹ symbols, which can be identical to or different from oneanother, each represent a monovalent phenyl or naphthyl radicaloptionally substituted with one or more radicals chosen from: a linearor branched C₁-C₁₂, preferably C₁-C₆, alkyl radical, a linear orbranched C₁-C₁₂, preferably C₁-C₆, alkoxy radical, a halogen atom, an—OH group, a —COOH group, a —COO-alkyl ester group, where the alkyl partis a linear or branched C₁-C₁₂ preferably C₁-C₆, residue, and a group offormula —Y⁴—Ar², where the Y⁴ and Ar² symbols have the meanings givenimmediately below,

[0048] the Ar² symbols, which can be identical to or different from oneanother or Ar¹, each represent a monovalent phenyl or naphthyl radicaloptionally substituted with one or more radicals chosen from: a linearor branched C₁-C₁₂ preferably C₁-C₆, alkyl radical, a linear or branchedC₁-C₁₂ preferably C₁-C₆, alkoxy radical, a halogen atom, an —OH group, a—COOK group or a —COO-alkyl ester group, where the alkyl part is alinear or branched C₁-C₁₂, preferably C₁-C₆, residue,

[0049] the Ar³ symbols, which can be identical to or different from oneanother, each represent a divalent phenylene or naphthylene radicaloptionally substituted with one or more radicals chosen from: a linearor branched C₁-C₁₂, preferably C₁-C₆, alkyl radical, a linear orbranched C₁-C₁₂, preferably C₁-C₆, alkoxy radical, a halogen atom, an—OH group, a —COOH group or a —COC)-alkyl ester group, where the alkylpart is a linear or branched C₁-C₁₂, preferably C₁-C₆, residue,

[0050] t is; an integer equal to 0 or 1,

[0051] with the additional conditions according to which:

[0052] + when t=0, the Y symbol is then a Y¹ monovalent radicalrepresenting the group of formula:

[0053] where the Ar¹ and Ar² symbols have the meanings given above,

[0054] + when t=1:

[0055] ★ on the one hand, the Y symbol is then a divalent radical havingthe following meanings y² to Y⁴:

[0056] Y²: a group of formula:

[0057] where the Ar2 symbol has the meanings given above,

[0058] Y³: a single valency bond,

[0059] Y⁴: a divalent residue chosen from:

[0060] a linear or branched C₁-C₁₂, preferably C₁-C₆, alkylene residueand a residue of formula —Si(CH₃)₂O—,

[0061] ★ on the other hand, solely in the case where the Y symbolrepresents y³ or Y⁴, the Ar¹ and Ar² (terminal) radicals have, inaddition to the meanings given above, the possibility of being connectedto one another via the Y′ residue consisting of Y′¹, a single valencybond, or of Y′², a divalent residue chosen from the residues cited withrespect to the definition of Y⁴, which is inserted between the carbonatoms, facing each other, situated on each aromatic ring in the orthoposition with respect to the carbon atom directly bonded to the S⁺cation;

[0062] → 3.2. and/or at least one monosulphonium species having a singleS⁺ cationic centre per mole of cation and comprising, in the majority ofcases, species of formula:

[0063] in which Ar¹ and Ar² have the meanings given above with respectto the formula (III.1), including the possibility of connecting directlybetween them only one of the Ar¹ radicals to Ar² according to the wayindicated above with respect to the definition of the additionalcondition in force when t=1 in the formula (II) involving the Y′residue;

[0064] 4)-organometallic cations of formula (IV):

(L¹L²L³M)q⁺  (IV)

[0065] in which formula:

[0066] M represents a metal from group 4 to 10, in particular iron,manganese, chromium or cobalt,

[0067] L¹ represents a ligand bonded to the metal M via π electrons,which ligand is chosen from η³-alkyl, η⁵-cyclopentadienyl andη⁷-cycloheptatrienyl ligands and η⁶-aromatic compounds chosen fromoptionally substituted θ⁶-benzene ligands and compounds having from 2 to4 condensed rings, each ring being capable of contributing to thevalency layer of the metal M via 3 to 8 π electrons,

[0068] L² represents a ligand bonded to the metal M via π electrons,which ligand is chosen from η⁷-cycloheptatrienyl ligands and η⁶-aromaticcompounds chosen from optionally substituted η⁶-benzene ligands andcompounds having from 2 to 4 condensed rings, each ring being capable ofcontributing to the valency layer of the metal M via 6 or 7 π electrons,

[0069] L³ represents from 0 to 3 identical or different ligands bondedto the metal M via σ electrons, which ligand(s) is (are) chosen from COand NO₂ ⁺; the total electronic charge q of the complex to which L¹, L²and L³ and the ionic charge of the metal M contribute being positive andequal to 1 or 2;

[0070] □ the anionic entity of the said borate having the formula:

[BX_(a)R_(b)]⁻

[0071] in which formula:

[0072] a and b are integers ranging from 0 to 3 for a and from 1 to 4for b, with a+b=4,

[0073] the X symbols represent:

[0074] ★ a halogen atom (chlorine or fluorine) with a=0 to 3,

[0075] ★ an OH functional group with a=0 to 2,

[0076] the R symbols are identical or different and represent:

[0077] a phenyl radical substituted by at least one electron-withdrawinggroup, such as, for example, OCF₃, CF₃, NO₂ or CN, and/or by at least 2halogen atoms (very particularly fluorine), this being when the cationicentity is an onium of an element from groups 15 to 17,

[0078] a phenyl radical substituted by at least one electron-withdrawingelement or group, in particular a halogen atom (very particularlyfluorine), CF₃, OCF₃, NO₂ or CN, this being when the cationic entity isan organometallic complex of an element from groups 4 to 10,

[0079] an aryl radical comprising at least two aromatic nuclei, such as,for example, biphenyl or naphthyl, which is optionally substituted by atleast one electron-withdrawing element or group, in particular a halogenatom (very particularly fluorine), OCF₃, CF₃, NO₂ or CN, whatever thecationic entity;

[0080] (2i) the POS comprises at least one monomer and/or one oligomerand/or one polymer selected:

[0081] from compounds comprising at least one (organo)functionalbridging group crosslinkable by the cationic route (G_(f) _(p) ) with aheterocyclic nature having one or more electron-donating atoms, such asO, S, N and P,

[0082] and/or from those comprising at least one ethylenicallyunsaturated G_(f) _(p) group which is substituted by at least oneelectron-donating atom which increases the basicity of the π system,

[0083] epoxidized POSs and/or POSs carrying vinyl ether groups beingparticularly preferred as G_(f) _(p) , and

[0084] (3i) the G_(f) _(p) s are present in a proportion (expressed ineq per kg of POS) of at least 0.01, preferably at least 0.10, and morepreferably still in a proportion of 0.15 to 2.00.

[0085] The present invention therefore proceeds from a novel andinventive advantageous selection of a specific class of siliconecompositions crosslinkable by the cationic route, preferably under UVradiation, which is marked out by the nature of its (photo)initiator ofthe onium borate or borate of organometallic cations type with a boratecounteranion of the borophenyl substituted by electron-withdrawing, forexample fluorinated, groups type, as well as by a specific POSexhibiting an appropriate level of G_(f) _(p) functional bridginggroups.

[0086] Such a selection gives access to an entire series of attractiveadvantages, namely in particular:

[0087] the excellent stability (pot life) of the composition, the changein the viscosity of the latter remaining slight despite the presence ofthe initiator for several days, indeed even several months, afterpreparing the composition, provided that the latter is stored with lightexcluded;

[0088] a very good reactivity at ambient temperature;

[0089] a low cost price due to the low cost of the starting materialsand to the simplicity of the application/crosslinking process forimpregnation and/or varnishing;

[0090] good flexibility of use, it being possible for the reactivity,the stability, the viscosity and the coefficient of friction of thevarnish of the impregnating agent or of the varnish which isnon-crosslinked to be easily varied, to a large extent, by varying:

[0091] Δ the molar mass of the POS oil carrying G_(f) _(p) ,

[0092] Δ the concentration of initiator,

[0093] Δ as well as the G_(f) _(p) /POS molar ratio;

[0094] a coating process for the impregnation and/or the varnishingwhich is simple to employ, which is fast and which does not requiresophisticated and expensive equipment and which is therefore,ultimately, productive and profitable;

[0095] no need to resort to toxic products in the composition.

[0096] It should also be noted that the varnishes or the impregnationsobtained on sheet gaskets, in particular on cylinder head gaskets,exhibit a beautiful. appearance (absence of bubbles) and satisfy therequired qualities of antiadhesiveness, of leaktightness and ofcompressibility. Furthermore, the varnish and/or the impregnating agentwhich is crosslimited has good mechanical properties, resistance toabrasion as well as thermal behaviour, behaviour towards oils and moregenerally behaviour towards aggressive products, such as the coolingliquid, which are entirely satisfactory.

[0097] According to a preferred arrangement of the invention, the POSemployed exhibits G_(f) _(p) s of the epoxide and/or vinyl ether typeand is selected from the POSs which are:

[0098] → either linear or substantially linear and composed of units offormula (V), terminated by units of formula (VI),

[0099] → or cyclic and composed of units of formula (V):

[0100] in which formulae:

[0101] the R¹ symbols are alike or different and represent:

[0102] either a linear or branched C₁-C₆ alkyl radical which isoptionally substituted, advantageously by one or more halogens, thepreferred optionally substituted alkyl radicals being: methyl, ethyl,propyl, octyl and 3,3,3-trifluoropropyl,

[0103] or an optionally substituted C₅-C₆ cycloalkyl radical,

[0104] or an aryl or aralkyl radical which is optionally substituted:

[0105] in particular by halogens and/or alkoxys,

[0106] phenyl, xylyl, tolyl and dichlorophenyl radicals being veryparticularly selected,

[0107] and, more preferably still, at least 60 molar % of the R¹radicals being methyls,

[0108] the Z symbols are alike or different and represent:

[0109] either the R¹ radical,

[0110] or a G_(f) _(p) group corresponding to an epoxide or vinyl etherresidue connected to the silicon via a divalent radical advantageouslycomprising from 2 to 20 carbon atoms optionally comprising a heteroatom,

[0111] at least one of the Z symbols corresponding to a G_(f) _(p)group.

[0112] Mention may be made, as examples of G_(f) _(p) organofunctionalgroups of the epoxy type, of those of the following formulae:

[0113] Mention may be made, as regard G_(f) _(p) organofunctional groupsof the vinyl ether type, of, e.g., those present in the followingformulae:

[0114] —(CH₂)₃—O—CH═CH₂, —(CH₃)₂—O—R⁴—O—CH═CH₂, —(CH₂)₃—O—CH═CH—R⁵ withR⁴=

[0115] linear or branched C₁-C₁₂ alkylene which is optionallysubstituted,

[0116] or arylene, preferably phenylene, which is optionallysubstituted, preferably by one to three C₁-C₆ alkyl groups;

[0117] with R⁵=linear or branched C₁-C₆ alkyl.

[0118] The POS used has a viscosity η (expressed in mPa.s at 25° C.),the value of which can vary substantially as a function of theapplication conditions and of the nature of the gaskets to be treated.

[0119] In the case of the treatment of a gasket which has already beencoated or of the application of a thin coating, use will advantageouslybe made of a POS having a low viscosity of between:

[0120] → 200 and 3000,

[0121] → preferably 300 and 2000,

[0122] → and more preferably still between 400 and 900.

[0123] In the case of the treatment of an uncoated gasket or of theapplication of a thicker coating, use will advantageously be made of aPOS having a higher viscosity of between:

[0124] → a value greater than 3000 and 10,000,

[0125] → preferably: a value greater than 3000 and 6000,

[0126] → and more preferably still: a value greater than 3000 and 5000.

[0127] These viscosity values relate both to the linear POSs and thecyclic POSs which can be employed in accordance with the use accordingto the invention.

[0128] The dynamic viscosity at 25° C. of all the silicone polymersconsidered in the present account can be measured using a Brookfieldviscometer according to AFNOR Standard NFT 76 102 of February 1972.

[0129] The viscosity with which the present account is concerned is thedynamic viscosity at 25° C., known as the “Newtonian” viscosity, that isto say the dynamic viscosity which is measured, in a way known per se,at a sufficiently low shear rate gradient for the viscosity measured tobe independent of the rate gradient.

[0130] In accordance with the invention, it is perfectly possible toenvisage the use of a mixture of different products possessing units offormulae (V) and (VI) as defined above (linear and/or cyclic).

[0131] The preferred epoxyfunctional or vinyloxyfunctionalpolyorganosiloxanes are disclosed in particular in PatentsDE-A-4,009,889; EP-A-0,396,130, EP-A-0,355,381; EP-A-0,105,341;FR-A-2,110,115 and FR-A-2,526,800.

[0132] The epoxyfunctional polyorganosiloxanes can be prepared by ahydrosilylation reaction between oils possessing Si—H units andepoxyfunctional compounds, such as, for example, 4-vinylcyclohexeneoxide or allyl glycidyl ether.

[0133] The vinyloxyfunctional polyorganosiloxanes can be prepared by thehydrosilylation reaction between oils possessing Si—H units andvinyloxyfunctional compounds, such as, for example, allyl vinyl ether or(allyl)vinyloxyethoxybenzene.

[0134] As regards the initiator, which is in practice a photoinitiator(PI) since the activation of the crosslinking preferably takes placeunder UV radiation, it is preferable to employ in accordance with theinvention a PI comprising a borate anionic entity selected from thefollowing group:

[B(C₆F₅)₄]⁻

[B(C₆H₄CF₃)₄]⁻

[B(C6H₃(CF₃)₂)₄]⁻

[(C₆F₅)₂BF₂]⁻

[C₆F₅BF₃]⁻

[B(C₆H₃F₂)₄]⁻,

[B(C₆F₄OCF₃)₄]⁻

[0135] and their mixtures.

[0136] As regards the cationic entity of the photoinitiator, thefollowing are distinguished:

[0137] 1) onium cations of formula (I)

[0138] 2) oxoisothiochroumaium cations of formula (II)

[0139] 3) mono- and/or polysulphonium cations of formula (III.1) and/or(III.2)

[0140] 4) organometallic cations of formula (IV).

[0141] The first counteranions of type 1) are disclosed in numerousdocuments, in particular in U.S. Pat. Nos. 4,026,705, 4,032,673,4,069,056, 4,136,102 and 4,173,476. The following cations will veryparticularly be favoured among these

[(Φ)₂I]⁺

[C₈H₁₇—O-Φ-I-Φ]⁺

[(Φ-CH₃)₂I]⁺

[C₁₂H₂₅-Φ-I-Φ]⁺

[C₈H₁₇—O-Φ)₂I]⁺

[C₈H₁₇—O-Φ-I-Φ)]⁺

[(Φ)₃S]⁺

[(Φ)₂-S-Φ-O—C₈H₁₇]⁺

[(CH₃-Φ-I-Φ-CH(CH₃)₂]⁺

[Φ-S-Φ-S-(Φ)₂]⁺

[(C₁₂H₂₅-Φ)₂I]⁺

[(CH₃-Φ-I-Φ-OC₂H₅]⁺

[0142] As regards the second family of cationic entities of formula (II)of oxoisothiochromanium type, it preferably comprises cationscorresponding to the structure D₁, which is defined on page 14 ofApplication WO-A-90/11303 and possesses the formula (II):

[0143] where the R⁶ radical has the meaning given in this WO applicationwith respect to the R¹ symbol; a cationic entity of this type which ismore preferred is that where R⁶ represents a linear or branched C₁-C₂₀alkyl radical. Mention will in particular be made, asoxoisothiochromanium salts which are particularly well suited, of thesulphonium salt of 2-ethyl-4-oxoisothiochromanium or of2-dodecyl-4-oxoisothiochromanium.

[0144] As regards the cationic entities 3), it will be specified thatthe polysulphonium cationic entity preferably comprises a species or amixture of species of formula (III.1), in which formula:

[0145] the Ar¹ radicals, which are identical to or different from oneanother, each represent a phenyl radical optionally substituted by alinear or branched C₁-C₄ alkyl radical or by the group of formula:

[0146] the Ar² radicals, which are identical to or different from oneanother and Ar¹, each represent a phenyl radical optionally substitutedby a linear or branched C₁-C₄ alkyl radical,

[0147] the Ar³ radicals each represent an unsubstituted para-phenyleneradical,

[0148] t is equal to 0 or 1,

[0149] with the additional conditions according to which:

[0150] + when t =0,

[0151] where the Ar¹ and Ar² radicals have the preferred meanings givenimmediately above in the present paragraph;

[0152] + when t=1:

[0153] ★ on the other hand, Y=Y² to Y⁴, with:

[0154] Y²=

[0155] where the Ar² radical has the preferred meaning given immediatelyabove in the present paragraph,

[0156] Y³=a valency bond,

[0157] Y⁴=—O— or —S—, and

[0158] ★ on the other hand, when Y=Y³ or Y⁴ and when it is then desiredto employ Ar¹ and Ar² (terminal) radicals connected to one another, a Y′bond is inserted consisting of a valency bond or the —O— residue.

[0159] The monosulphonium species, when some are present, which enterinto the context of this preferred form are the species of formula(III.2) in which the Ar¹ and Ar² symbols have the preferred meaningsindicated above in the preceding paragraph, including, when theseradicals are directly connected to one another via a Y′ residue, theinsertion of a valency bond or of the —O— residue.

[0160] Mention may particularly be made, as examples of sulphoniumcationic entities, of:

[0161] the mixtures, in variable amounts, of the species 5+2+optionally3,

[0162] the mixtures, in variable amounts, of the species 5 with thespecies 10 of formula:

[0163] The borate anionic entity is preferably chosen from the anions offormula [BX_(a)R_(b)]⁻, in which:

[0164] the X symbols represent a fluorine atom,

[0165] the R symbols , which are identical or different, represent aphenyl radical substituted by at least one electron-withdrawing groupchosen from OCF₃, CF₃, N0₂ and CN and/or by at least two fluorine atoms.

[0166] The borate anionic entity of formula [BX_(a)R_(b)]⁻ isadvantageously chosen from the following anions:

[B(C₆F₅)₄]⁻  1′

[(C₆F₅)₂BF₂]⁻  2′

[B(C₆H₄CF₃)₄]⁻  3′

[B(C₆F₄OCF₃)₄]⁻  4′

[B{C₆H₃(CF₃₎ ₂}₄]⁻  5′

[B(C₆H₃F₂)₄]⁻  6′

[0167] The novel polysulphonium borates which will very preferably beemployed are the salts formed by the combination of the followingcations and anions: Cation Anion 5 1′ 5 3′ 5 4′ 5 + 10 mixtures 1′ 5 +10 mixtures 3′ 5 + 10 mixtures 4′

[0168] These polysulphonium borates can be prepared by an exchangereaction between a salt of the cationic entity (halide, such as, forexample, chloride or iodide) and an alkali metal (sodium, lithium orpotassium) salt of the anionic entity.

[0169] The operating conditions (respective amounts of reactants, choiceof the solvents, duration, temperature and stirring) are within thescope of a person skilled in the art; these must make it possible torecover the desired polysulphonium borate in the solid form, byfiltration of the precipitate formed, or in the oily form, by extractionusing an appropriate solvent.

[0170] The procedures for the synthesis of the halides of the cationicentities of formula (III.1) are described in particular in: “PolymerBulletin (Berlin)”, Vol. 14, pages 279-286 (1985) and U.S. Pat. No.4,400,541.

[0171] According to one alternative relating to the preparation of thepolysulphonium borates, the latter can be prepared directly by reactionbetween a diaryl sulphoxidle and a diaryl sulphide according to theteaching described in: “J. Org. Chem”, Vol. 55, pages 4222 -4:25 (1990).

[0172] These novel polysulphonium borates can be employed in the statein which they are obtained on conclusion of their preparation process,for example in solid or liquid form or in solution in an appropriatesolvent, in compositions comprising monomers/oligomers/polymers whichare intended to be polymerized and/or crosslinked by the cationic routeand under activation, for example UV activation.

[0173] The monosulphonium species (III.2) dealt with above can be inparticular the coproducts which are formed during the preparation of thepolysulphonium cations, the presence of which can be more or lessavoided.

[0174] Up to 99%, more generally up to 90% and more generally still upto 50% by mole (of cation) of the polysulphonium species of formula(III.1) can be replaced by monosulphonium species (III.2).

[0175] As regards the fourth type of cationic entity, it is founddisclosed in Patents U.S. Pat. No. 4,973,722 and U.S. Pat. No. 4,992,572and European Patent Applications EP-A-203,829, EP-A-323,584 andEP-A-354,181. The organometallic cations more readily used practice arein particular:

[0176] (η⁵-cyclopentadienyl) (η⁶-toluene)Fe⁺

[0177] (η⁵-cyclopentadienyl) (η⁶-1-methyl-naphthalene)Fe⁺

[0178] (η⁵-cyclopentadienyl) (η6-cumene)Fe⁺

[0179] bis(η⁶-mesitylene)Fe⁺

[0180] bis (η⁶-benzene) Cr⁺

[0181] It results from the above that the preferred photoinitiatorsaccording to the invention are those corresponding to the followingformulae:

[(Φ)₂I]⁺[B(C₆F₅)₄]⁻

[(C₈H₁₇)—O-Φ-I-Φ]⁺[B(C₆F₅)₄]⁻

[(C₁₂H₂₅-Φ-I-Φ]⁺[B(C₆F₅)₄]⁻

[(C₈H₁₇—O-Φ)₂I]⁺[B(C₆F₅)₄]⁻

[(C₈H₁₇)—O-Φ-I-Φ]⁺[B(C₆F₅)₄]⁻

[(Φ)₃S]⁺[B(C₆F₅)₄]⁻

[(Φ)₂S-Φ-O—C₈H₁₇]⁺[B(C₆H₄CF₃)₄]⁻

[(C₁₂H₂₅-Φ)₂I]⁺[B(C₆F₅)₄]⁻

[(Φ)₃S]⁺[B(C₆F₄OCF₃)₄]⁻

[(Φ-CH₃)₂I]⁺[B(C₆F₅)₄]⁻

[(Φ-CH₃)₂I]⁺[B(C₆F₄OCF₃)₄]⁻

[0182] (η⁵-cyclopentadienyl) (η⁶-toluene)Fe⁺[B(C₆F₅)₄]⁻

[0183] (η⁵-cyclopentadienyl) (η⁶-1-methylnaphthalene) Fe⁺[B(C₆F₅)₄]⁻

[0184] (η⁵-cyclopentadienyl) (η⁶-cumene)Fe⁺[B(C₆F₅)₄]⁻

[0185] Mention may be made, as other literature reference in definingthe onium borates 1) and 2) and the borates of organometallic cations4), which are selected as photoinitiator in the context of the cylinderhead gasket use according to the invention, of the entire contents ofEuropean Patent Applications No. 0,562,897 and 0,562,922. These contentsare incorporated in full by reference in the present account.

[0186] The initator salts of type 1) and 2) employed in the context ofthe use according to the present invention can be prepared by anexchange reaction between a salt of the cationic entity (halide, suchas, for example, chloride, iodide, hexafluorophosphate,tetrafluoroborate or tosylate) and an alkali metal (sodium, lithium orpotassium) salt of the anionic entity.

[0187] The operating conditions (in particular respective amounts ofreactants, choice of the solvents, duration, temperature and stirring)are within the scope of a person skilled in the art; these must make itpossible to recover the desired initiator salt in the solid form, byfiltration of the precipitate formed, or in the oily form, by extractionusing an appropriate solvent.

[0188] The alkali metal salts of the anionic entity can be prepared in aknown way by an exchange reaction between a haloboron compound and anorganometallic compound (for example a magnesium, lithium or tincompound) carrying the desired hydrocarbon-comprising groups, in astoichiometric amount, optionally followed by hydrolysis using anaqueous alkali metal halide solution; this type of synthesis is, forexample, disclosed in “J. of Organometallic Chemistry”, Vol. 178, p.1-4, 1979; “J.A.C.S.”, 82, 1960, 5298; “Anal. Chem. Acta”, 44, 1969,175-183; U.S. Pat. No. 4,139,681 and DE-A-2,091,367; and “Zh. Org.Khim.”, Vol. 25, No. 5, pages 1099-1102, May 1989.

[0189] The preparative method for the salts of the cationic entity 4) offormula (IV) is disclosed in particular in D. Astruc, TetrahedronLetters, 36, p. 3437 (1973); D. Astruc, Bull. Soc. Chim. Fr., 1-2, p.228 (1976); D. Astruc, Bull. Soc. Chim. Fr., 11-12, p. 2571 (1975); D.Astruc, CR Acad. Sc. Paris, part C, 272, p. 1337 (1971); A. N.Nesmeyanov et al., Izves, Akad. Nauk SSSR, ser. Khim., 7, p. 1524(1969); A. N. Nesmeyanov et al., Dokl. Akad. Nausk SSSR, 160 (6), p.1327 1965); A. N. Nesmeyanov et al., Dokl. Akad. Nausk SSSR, 149 (3), p.615 (1963).

[0190] In practice, the initiators of the use according to the inventionare prepared in a very simple way by dissolution of the onium borate ororganometallic complex borate, preferably onium borate, which areprovided in the solid (powder) form, in a solvent.

[0191] According to an alternative relating to the onium borate, thelatter can be prepared directly in the solvent from a salt (e.g.,chloride) of the cation (iodonium) and from a salt (for example,potassium) of the borate anion.

[0192] Preferably, it is planned, in accordance with the use accordingto the invention, for the initiator (PI) to be employed in solution inan organic solvent, preferably chosen from proton-donating solvents andmore preferably still from the following group: isopropyl alcohol,benzyl alcohol, diacetone alcohol, esters of hydroxylated carboxylicacid, such as, for example, butyl lactate, and their mixtures.

[0193] It should be specified that the term “effective catalytic amountof PI” is understood to mean, within the meaning of the invention, theamount sufficient to initiate the crosslinking.

[0194] As far as practicable, as indicated above, the photoinitiator isadvantageously dissolved in a polar solvent, in an amount such that itscontent in the solution obtained is between 1 and 50% by weight,preferably between 10 and 30% by weight and more preferably stillbetween 15 and 25% by weight.

[0195] According to an advantageous form of the use according to theinvention, the incorporation of the PI in solution in the compositioncomprising the POS possessing a given molar content of G_(f) _(p) iscarried out in a proportion of 0.1 to 10% by weight of solution withrespect to the final mixture, preferably 0.5 to 5% by weight and morepreferably of the order of 1% by weight.

[0196] In addition to the specific photoinitiator or photoinitiators ofborate 1) to 4) type, the initiator system can comprise, according to anadvantageous alternative form, at least one photosensitizer selectedfrom (poly)aromatic products, which are optionally metallic, andheterocyclic products and preferably from the following list ofproducts: phenothiazine, tetracene, perylene, anthracene,9,10-diphenyl-anthracene, thioxanthone, benzophenone, acetophenone,xanthone, fluorenone, anthraquinone, 9,10-dimethyl-anthracene,2-ethyl-9, 10-dimethyloxyanthracene, 2,6-dimethylnaphthalene, 2,5-diphenyl-1, 3, 4-oxadiazole, xanthopinacol, 1, 2-benzanthracene,9-nitroanthracene and their mixtures.

[0197] According to one alternative form of the use in accordance withthe invention, use may be made of crosslinking inhibitors, preferablychosen from alkaline products and more preferably still from alkalineproducts of amino type, for example of the type of those consisting of asilicone onto which is grafted at least one amine group, preferably atertiary amine.

[0198] It is possible to resort to other additives known in this type ofapplication of silicone compositions crosslinkable under UV radiation bythe cationic route. Examples of these other additives will be givenhereinbelow in a part of the present account relating to thecompositions.

[0199] Systems for the preparation of antiadhesive coatings bycrosslinking of a film of a silicone composition, by exposure toultraviolet radiation and according to a crosslinking mechanism of thecationic chain reaction type, are known, as revealed in particular inthe abovementioned European Patent Applications No. 0,562,897 and No.0,562,922. However, until now, the exploitation of such systems or ofsuch compositions for the coating (impregnation/varnishing) of sheetgaskets, in particular of cylinder head gaskets, by selecting POSshaving specific levels of G_(f) _(p) crosslinking groups of epoxy orvinyl ether type, for example, had never been imagined.

[0200] The advantages of these systems are:

[0201] few or no solvents. This results in slight pollution and a lowcost.

[0202] rapid crosslinking, resulting in high productivity.

[0203] weak heating, resulting in the possibility of broadening thespectrum of supports which can be envisaged.

[0204] low energy consumption, resulting in a substantial saving.

[0205] methodological simplicity and a simple device, which limit thecost of the industrial investments required.

[0206] In the case where it is employed as a varnish, the siliconecomposition selected in accordance with the invention is applied to asupport formed by a sheet gasket, in particular a cylinder head gasket,rendered leaktight by impregnation using a silicone and/or coated with asilicone elastomer layer intended to form, for example, the gasket curb.

[0207] Thus, in accordance with an alternative form of the invention,the support receiving the silicone coating obtained by crosslinking bythe cationic route is a sheet gasket, in particular a cylinder headgasket:

[0208] ∘ which is preimpregnated with at least one material forrendering leaktight formed by at least one crosslinked polymer,preferably by at least one silicone resin,

[0209] ∘ and/or which is precoated with at least one layer of at leastone elastomer preferably selected from crosslinked or non-crosslinkedsilicone elastomers and their mixtures.

[0210] In other words, the varnishing using the selected siliconecomposition can be carried out either directly on the bare surface ofthe sheet gasket, in particular of the cylinder head gasket, whateverits nature, or on the sheet gasket, in particular the cylinder headgasket, impregnated with a crosslinked silicone resin of thecondensation or polyaddition type, or on a sheet gasket, in particular acylinder head gasket, impregnated with a crosslinked silicone resin andcovered with a crosslinked or non-crosslinked silicone resin forming,for example, the gasket curbs.

[0211] The coating according to the invention can therefore be appliedto any metallic, composite (kevlar, graphite), silicone elastomer,fluorinated elastomer, of the Viton type, or NBR elastomer support.

[0212] The sheet gasket (in particular cylinder head gasket) varnishformed by the coating obtained by crosslinking by the cationic route isadvantageously mono- or multilayer and exhibits a thickness of:

[0213] between 1 and 100 μm

[0214] preferably between 5 and 50 μm

[0215] and more preferably still between 10 and 20 μm.

[0216] According to another of these aspects, the present inventionrelates to a process for carrying out impregnation(s) and/or forpreparing coating(s) which is (are) antiadhesive at the engineblock/cylinder head interface of engines on supports composed of sheetgaskets, in particular cylinder head gaskets, characterized in that itconsists essentially in employing a composition which is crosslinkableunder the effect of light radiation and optionally under the effect ofheat, the said composition and the support being those as defined above.

[0217] The present invention also relates to a sheet gasket, inparticular a cylinder head gasket, characterized in that it isimpregnated and/or coated with a matrix obtained by crosslinking by thecationic route in accordance with the use as defined above and/or withthe process as described above.

[0218] Any silicone composition crosslinkable by the cationic route,characterized in that it is intended for carrying out impregnation(s)and/or for preparing coating(s) which is (are) antiadhesive on sheetgaskets, in particular cylinder head gaskets, and in that it comprises:

[0219] at least one POS possessing G_(f) _(p) groups as defined above,

[0220] at least one initiator, preferably a photoinitiator (PI), of anonium borate type as defined above,

[0221] at least one solvent of the PI as defined above,

[0222] and at least one additive chosen from those generally employed intreatments targeted at rendering leakproof and antiadhesive the cylinderhead/engine block interface and in particular sheet gaskets, such as,especially, cylinder head gaskets,

[0223] also comes within the scope of the invention.

[0224] The various additives specific to the targeted final application,namely sheet gaskets and in particular cylinder head gaskets, are, e.g.,one or more crosslinking inhibitors preferably chosen from alkalineproducts and more preferably still from alkaline products of amino type,for example of the type of those consisting of a silicone onto which isgrafted at least one amine group, preferably a tertiary group, oralternatively of the type of those comprising a piperidinyl residuewhich is optionally alkyl-substituted.

[0225] The compositions according to the invention can also comprise:

[0226] adhesion modifiers (linear silicone resins or polymers carrying,for example, vinyl, epoxy, vinyl ether or alcohol functional groups),such as, for example, those disclosed in European Patent Application No.0,738,769;

[0227] one or more photosensitizers of the type of those mentionedabove,

[0228] one or more fillers, such as, for example: inorganic fillers,such as in particular milled natural or synthetic (polymer) fibres,calcium carbonate, talc, clay, titanium dioxide, or precipitation orcombustion silica;

[0229] one or more polymerization and/or crosslinking acceleratorspreferably chosen from hydroxylated carboxylic acid esters which areliquid at ambient temperature (23° C.);

[0230] one or more thixotroping agents;

[0231] and their mixtures.

[0232] Likewise, soluble dyes, oxidation inhibitors and/or any othermaterial which does not interfere with the catalytic activity of thephotoinitiator and which does not absorb in the wavelength range chosenfor the photoactivation can also be added to the composition or employedin the context of the process according to the invention.

[0233] These compositions in accordance with the invention are prepared,without distinction, before (indeed even long before) or elseimmediately before use.

[0234] It should be noted that these compositions are particularlystable on storage and that they offer, in accordance with the process ofthe invention, rapid crosslinking kinetics. In addition, theirnon-crosslinked state, before exposure to the activating lightradiation, makes them very easy to handle, to apply or to position onsheet gaskets, such as, in particular, cylinder head gaskets.

[0235] The process according to the invention which makes it possible torender sheet gaskets, in particular cylinder head gaskets, non-adhesiveconsists in applying an amount of composition of the invention,generally of between 2.5 and 250 g per m² of surface to be coated, andin crosslinking the composition by supplying energy, at least a portionof which, preferably all of which, is provided by UV radiation.

[0236] The UV radiation used exhibits a wavelength of between 200 and400 nanometers, preferably of between 254 and 360 nanometers.

[0237] The duration of irradiation can be short and it is generally lessthan 1 second and is of the order of a few hundredths of a second forvery thin coatings. The crosslinking achieved is excellent, even in theabsence of any heating. Of course, the coupling of the photoactivationto a thermal activation, e.g. by heating between 25 and 100° C., is notexcluded from the invention.

[0238] Of course, the curing time can be adjusted, in particular by thenumber of UV lamps used, by the duration of exposure to the UV radiationand by the distance between the composition and the UV lamp.

[0239] The amounts of compositions deposited on the supports arevariable and generally range between 2.5 and 250 g/m² of surfacetreated. These amounts depend on the nature of the supports and on thedesired antiadhesive properties. They are generally between 10 and 50g/m² for non-porous supports.

[0240] The following examples are given by way of illustration andcannot be regarded as a limit on the field and spirit of the invention.

EXAMPLES I-Starting Materials I.1. The FunctionalizedPolyorganosiloxanes (UV RESIN) Employed are(1,2-epoxycyclohex-4-ylethyl) -polydimethylsiloxanes of formula:

[0241]

[0242] Several POSs having different epoxy levels are prepared.

[0243] This synthesis is carried out in the following way:

[0244] The silicone oil employed is a polydimethylhydrosiloxane (PDMS)of following simplified formula: M₂D′_(a)D_(b)

[0245] → the VCMX=

[0246] sold by Union Carbide.

[0247] → The catalyst=Karstedt Pt comprising 10% of Pt indivinyltetramethyldisiloxane; this catalyst can be used as required as amixture with a Pt-inhibiting agent consisting of thiodiethanol.

[0248] → The A21 resin is an Amberlite exchange resin.

→ METHODOLOGY

[0249] PHASE I: HYDROSILYLATION PHASE

[0250] ⅓ of the SiH silicone oil is charged under N₂ (1st part)

[0251] the VCMX is charged with stirring

[0252] the catalyst: 10% Karstedt Pt, is charged

[0253] the mixture is slowly heated to 60° C. under N₂

[0254] the 2nd part of the silicone oil is charged while maintainingθ=60-80° C. (duration of introduction: 0.5 to 1 h)

[0255] the reaction mixture is maintained until a maximum DC_(SiH) % isachieved (residual SiH <300 ppm)

[0256] PHASE II REMOVAL OF THE Pt

[0257] the A21 resin (milled, dried) is charged

[0258] the mixture is maintained at 60°-80° C. until maximumdecoloration of the medium is obtained (duration ≧10 hours in order toobtain <100 hazen units)

[0259] the mixture is filtered in order to remove the ion exchange resin

[0260] PHASE III: REMOVAL OF THE LIGHT PRODUCTS

[0261] the mixture is devolatilized under vacuum: 120/125° C., 5 mm Hg,under N₂ stripping, in order to remove the silicone oligomers and theexcess VCMX.

[0262] a final clarification is carried out in order to remove possiblemicrogels formed during the preceding stage. Yield of final polymerrecovered≈90%. Data by weight Units by weight A B C D E Products chargedTotal 93.6 105.9 99.37 86.64 95.25 silicone oil VCMX 14.7 2.38 8.9321.66 13.05 Catalyst 8.4 × 10⁻³ 8.4 × 10⁻³ 8.4 × 10⁻³ 8.4 × 10⁻³ 8.4 ×10⁻³ A21 Resin 0.64 0.64 0.64 0.64 — Thiodi- — — — — 10.8 ethanolProducts extracted Volatiles 8.1 7.8 8.3 8.2 7.9 Final 100 100 100 100100 polymer

[0263] The POSs A, B, C, D and E thus obtained are defined in the tablebelow: Level of G_(fp) epoxide/POS (in η at 25° C. POS a b equivalentper kg) (in mPa · s) A 7 85 0.90 350 B 3 240 0.16 780 C 6 123 0.58 580 D11 63 1.60 580 E 27 343 0.88 4600

I.2. The Initiator (Hereinafter Known as Photoinitiator PI) is OniumBorate: Ditolyliodonium Tetrakisi(Pentafluorophenyl)Borate of Formula

[0264]

[0265] The cation of this onium borate is prepared according to thegeneral methodology disclosed in European Patent Applications Nos.0,562,922 and 0,562,897. The procedure as regards the borate anionicentity is as follows:

[0266] Bromopentafluorobenzene (21.3 g, 0.086 mol) and isopropyl etherare charged, under an inert atmosphere, to a 500 ml round-bottomed flaskequipped with mechanical stirring, a reflux condenser and a droppingfunnel. The mixture is stirred and is cooled to a temperature of −78° C.using an acetone+dry ice bath.

[0267] n-Butyllithium, in solution in hexane (1.6M, 52.3 ml, 0.97 eq),is charged to the dropping funnel and is then added over approximately10 minutes. The mixture is subsequently left stirring at a temperatureof −78° C. for 30 min. The dropping funnel is replaced by a droppingfunnel comprising boron trichloride in solution in hexane (1.0M, 19 ml).The boron trichloride is added over 15 min and then the reaction mixtureis left stirring at a temperature of −78° C. for 30 min. The mixture issubsequently allowed to return to room temperature over approximately 1h. A saturated aqueous KCl solution (100 ml) is then added. The mixturethen has two phases and is homogeneous. The isopropyl ether is distilledoff. The KB(C₆F₅)₄ precipitates at the end of distillation. It isrecovered by filtration and is then washed with a saturated KCl solution(100 ml) before being dried under vacuum at a temperature of 35° C.

[0268] A product assaying 97% of expected product is thus obtained, witha yield of 99%.

[0269] The solvents used are isopropyl alcohol, butyl lactate, esters ofdiacetone alcohol or their mixtures.

[0270] The photoinitiator system is prepared by dissolving the oniumborate (optionally complemented with a portion of the epoxidized PDMS tobe employed) in the solvent.

II. The General Procedure Followed is as Follows

[0271] x part by weight of a solution of onium borate in a solvent(assay 18% by weight) is added

[0272] to 100 parts by weight of epoxidized PDMS,

[0273] and mixing is carried out by manual stirring for 30 minutes.

III - Equipment III.1 Type of UV Lamp: FUSION SYSTEM® F450 Technology(Company Fusion)

[0274] Total power of the lamp: 120 watts

[0275] The emitter of the UV lamp is composed of a transparent quartztube filled with mercury. The UV radiation is produced by excitation ofthe emitter with microwaves and magnetons, thus causing the evaporationof the mercury and the emission of UV radiation: UV Fusion system.

III.2 Characteristics of the UV Bench

[0276] The UV bench belt can reach a maximum speed of forwardprogression of the order of 52 m/min. The speed of this bench can beadjusted according to the requirements of the user or of the nature ofthe product to be crosslinked.

III.3 Meyer Bar

[0277] A Meyer bar is used to deposit a thin film on the gaskets. Thisbar contains grooves along its shaft which make it possible, afterapplication of the resin, to obtain the desired thickness. Deposition iscarried out automatically using an electric motor, with which it ispossible to vary the rate of passage of the bar over the gasket.

III.4 Cylinder Head Gaskets

[0278] The tests were carried out on conventional “soft” gaskets (boardgaskets) originating from the “Payen” group or from “Meillor gasket”.

[0279] These board gaskets are composed of a block of composite fibres(generally based on Kevlar) which is sandwiched and fastened to a wiremesh.

EXAMPLE 1 Influence of the Content of Photoinitiator on the Shore AHardness of the Resin Obtained by Crosslinking Under UV Radiation of anEpoxyfunctionalized POS A

[0280] The POS employed is POS A.

[0281] The PI is dissolved in a proportion of 18% by weight in butyllactate.

[0282] The POS comprises an inhibitor with the function of increasingthe pot life of the resin. It is present at a level of 50 ppm in thePOS. In all the examples, this inhibitor is composed of a tertiary aminesold under the trade name Tinuvin 765 by the company Ciba-Geigy(1,2,2,6,6-pentamethyl-4-piperidyl derivative).

[0283] The methodology used is that described in the preamble of theexamples.

[0284] The Shore A hardness measurements were carried out at differentlevels of photoinitiator solution, 1%, 1.5%, 2%, 2.5% and 3% (resin withinhibitor and photoinitator in butyl lactate). Two repeatability testswere carried out (Tests 1 and 2).

[0285] The reference is formed by a two-component polyaddition resin(part A and part B mixed at 50/50 by weight).

[0286] The part A is composed of a vinylated silicone oil and of aplatinum catalyst (2.5% of vinyl groups and 45 parts per million ofplatinum).

[0287] The part B is composed of a mixture of different vinylated orhydrogenated silicone oils and of a polymerization retarder “composed ofethynylcynclohexanol” (1.5% of vinyl groups and 20% ofpolymethylhydrosiloxane groups).

[0288] Results: TABLE 1 Weight % PI solution with Refer- respect to thePOS 1% 1.5% 2% 2.5% 3% ence Shore A hardness 78.4 74.7 76.4 76.3 74.574.2 Test 1 Shore A hardness 79.3 79.7 76.7 73.9 73.7 73.2 Test 2

[0289] Analysis:

[0290] The Shore A hardness is virtually identical, whatever thecomposition of the UV resin +% of photoinitiator mixture. It is spreadover a hardness range of between 74 and 80. It is slightly greater thanthe hardness of the reference resin. These results thus obtained provethat the resin has the same level of crosslinking, whatever theconcentration of PI.

EXAMPLE 2 Determination of the Konig Hardness 2.1. INFLUENCE OF THESPEED OF FORWARD PROGRESSION OF THE UV BENCH ON THE KÖNIG HARDNESS OFTHE RESIN WITH INHIBITOR COMPRISING DIFFERENT % OF PHOTOINITIATOR (BUTYLLACTATE)

[0291] The object of this study consists in monitoring, by virtue of theKönig hardness, the change in the crosslinking of the UV resin of type Aas a function of the duration of exposure to UV radiation and of theproportion of photoinitiator added. Coating was carried out with a Meyerbar No. 3 (thickness deposited approximately 20 μm) on paper. The resin,once crosslinked at different speeds of forward progression, issubsequently subjected to the König pendulum.

[0292] Results: TABLE 2 % PI in solution with 1% 1.5% 2% 2.5% 3% respectto the POS + PI König König König König König mixture hard- hard- hard-hard- hard- Speed ness ness ness ness ness 12.5% maxi speed 26.6 22.621.9 28.4 23.5 4 m/minute 25% maxi speed 29.4 25.2 24.9 24.1 19.6 11.5m/minute 50% maxi speed 23.4 22.4 23.1 21 24.1 28.1 m/minute 75% maxispeed 25.6 21 22.9 23.8 21 39.2 m/minute 100% maxi speed 28.7 22.4 24.723.3 24.1 52.1 m/minute

[0293] POS resin with 50 ppm of inhibitor composed of Tinuvin.

[0294] Analysis:

[0295] From the analysis of the table relating to the König hardness ofthe UV resin (with inhibitor) with different levels of photoinitiator(butyl lactate) as a function of the speed of the UV bench, it is foundthat the crosslinking takes place in all cases, whatever the percentageof photoinitiator and the speed, even for a low content ofphotoinitiator and a maximum speed on the UV bench. The König hardnessvalues, independently of the % of photoinitiator and of the speed of theUV bench, lie between 19.6 and 29.4. However, it would seem that the 1%mixture has a better degree of crosslinking higher than the othermixtures, despite the variation in the speed of forward progression ofthe bench.

2.2. CHANGE OVER TIME OF THE KÖNIG HARDNESS OF THE RESIN A (WITHINHIBITOR) AND OF THE REFERENCE RESIN ON A METAL (STEEL) PLATE COATED ONONE SIDE WITH AN ADHESION PROMOTER

[0296] A metal plate, degreased beforehand, is coated on one side withan adhesion promoter or primer (4% isopropyl titanate in isopropylalcohol). The resin (resin A and reference resin) is subsequentlydeposited on each face and the change in the König hardness issubsequently monitored five days after application.

[0297] Results: TABLE 3 % by weight PI in solution 1st day 5th day withwithout 2nd day without 5th day respect to Primer with primer primerwith primer the POS + König König König König PI mixture hardnesshardness hardness hardness 2% 35.0 25.2 37.0 33.6 3% 39.2 31.4 45.6 33.9Reference 48.2 58.5 48.5 59.4

[0298] Analysis:

[0299] The König hardness of the reference resin is greater than that ofthe resin A. However, its value remains unchanged over time, after fivedays at ambient temperature. The adhesion promoter improves the hardnessin the case of the reference resin. As regards the resin A, the adhesionpromoter decreases the König hardness. The hardness of the resin Aincreases after five days at ambient temperature.

EXAMPLE 3 Monitoring of the Antiadhesiveness of the UV Resin

[0300] Principle: ASTM F 607-84 standard test

[0301] The antiadhesiveness test is carried out by using anextensometer. A thin film of POS A resin is applied, by coating byvirtue of a Meyer bar, to each face of a preimpregnated soft (or board)gasket. This resinous film, with an oily appearance, is subsequentlycrosslinked by passing under a UV bench, the speed of forwardprogression of the belt of which is 2.8 m/min, in order to ensure thatthe crosslinking is complete. In the case of the reference resin, thegasket, after coating with the Meyer bar, is, for its part, placedinside an oven calibrated at a temperature of 150° C. for approximately5 to 10 minutes.

[0302] After varnishing the gasket, the gasket is cut with a hollowpunch in order to form two circular disc-shaped test specimens (Ø 50 mm)comprising, on each of these faces, the antiadhesive varnish. Each discis placed between two supports made of G5 cast iron. A pressure of 10MPa is exerted, using a press, on the supports containing the circulargasket in order for the conditions to be those of the tightening of thecylinder head gaskets during the assembly of the engine. The pressure of10 MPa is achieved by tightening the screw bolts situated at the ends ofthe press using a spanner with a dynamometer attached.

[0303] All the presses comprising the varnished disc samples aresubsequently subjected to a temperature of 130° C. for 72 hours.

[0304] After a period of 72 hours in the oven at 130° C., the pressesare removed from the oven and left at ambient temperature for one day inorder to cool. They are subsequently dismantled in order to recover thesupports comprising the circular gaskets. These supports are insertedinto appropriate jaws of the extensometer, the role of which will be tomeasure the breaking force (in Newtons) which has to be exerted in orderto separate the two supports in which the gasket is imprisoned. This isbecause the varnishing resin deposited on the gasket can, as a result ofhaving been subjected to a temperature of 130° C. and a pressure of 10MPa for 72 hours, interact with the material of the supports, that is tosay adhere to the supports.

[0305] If the extensometer indicates a high breaking force, this meansthat the varnish adheres to the support and that the antiadhesiveness ofthe resin is low.

[0306] It sometimes happens that the supports automatically becomedetached during the dismantling of the press after the obligatory spellin the oven at 130° C. for 72 hours. This spontaneous detachment of theprevarnished gasket arises from the excellent antiadhesive property ofthe silicone resin which has been used for the coating. The adhesion ofthe gasket is completely insignificant. It will therefore be acceptedthat the breaking force, resulting from the separating of two supportscomprising the gasket, is zero and that the antiadhesiveness capacity ofthe resin is considerable.

[0307] After the sample has failed on the extensometer, each supportwhich has been used for griping the gasket is analysed by the operatorin order to estimate the percentage of resin remaining attached. Thispercentage can be expressed as % of cohesive or adhesive failure. 100%of cohesive failure means that the gasket has adhered to the supportsuch that it has torn, dividing into two parts which remain bonded totheir initial contact support. 0% of cohesive failure corresponds toperfect antiadhesiveness of the resin on the supports; no trace of resinremains on the support after the sample has failed on the extensometer.

[0308] Results:

[0309] Resin tested=UV resin of type A with Tinuvin inhibitor (50 ppm)and reference resin

[0310] Coating: Meyer bar No. 3, thickness of approximately 15-20 μm

[0311] UV crosslinking: 1 passage under a UV bench, speed=10% (2.8 m/mn)

[0312] Crosslinking: Reference resin: 10-15 minutes at 150° C. with aconstant temperature rise from 70° C. to 150° C. TABLE 4 % PI insolution with respect to the Breaking Breaking POS + PI mixture force inN stress in MPa Type of failure 1% No. 1 274.1 0.140 90% adhesive 1% No.2 562.2 0.287 85% adhesive Mean 1% 418.2 0.213 85%-90% adhesive 2% No. 1493.1 0.251 80% adhesive 2% No. 2 503.4 0.257 70% adhesive Mean 2% 498.20.254 75% adhesive 3% No. 1 563.5 0.287 75% adhesive 3% No. 2 156.90.080 65% adhesive Mean 3% 360.2 0.184 70% adhesive Reference No. 1439.4 0.224 95% adhesive Reference No. 2 346.6 0.177 98% adhesive Meanreference 393.0 0.200 97% adhesive

[0313] Analysis:

[0314] If reference is made to Table 4, in which the antiadhesivenesstest values of the UV resin of type A and of the reference resin arecombined, the result is that the UV resin has approximately the sameantiadhesive capacity independently of the content of photoinitiator(mean value of the breaking force of between 498 and 360 N). Thisantiadhesiveness is comparable with that of the reference resin (meanvalue of the breaking force of 393 N). The antiadhesiveness of thereference resin is of the same order of magnitude as that of the UVresin.

CONCLUSION

[0315] The UV resin of type A (resin with Tinuvin inhibitor,,photoinitiator diluted in butyl lactate) has the same mechanicalproperties as the reference resin. The antiadhesiveness test has shownthat the % adhesive failure was close to 100% for the reference resinand that it is between 70% and 90%, as regards the UV resin, despite anequivalent breaking force.

EXAMPLE 4 Influence of the Presence of Inhibitor and of the ChemicalNature of the Diluent used for the Photoinitiator on theAntiadhesiveness 4. 1 UV resin of type A

[0316] Principle

[0317] In order to find out what were the influences of the inhibitorand of the diluent on the antiadhesiveness, a series of four mixtures(NRNC, NRAC, ARNC and ARAC) with a content of photoinitiator solution of2% was subjected to the antiadhesiveness test.

[0318] Results: cf. Table 5

[0319] Resins:

[0320] A Resin tested: Resin A (idem Examples 1 to 3) described in I.1.

[0321] A Reference resin (idem examples 1 to 3) described in Example 1.

[0322] inhibitor: Tinuvin (idem Examples 1 to 3).

[0323] Coating: Meyer bar No. 3, thickness of approximately 15-20 μm

[0324] UV crosslinking: 1 passage under a UV bench, speed=10% (2.8m/min)

[0325] Crosslinking: Reference resin: 10-15 minutes at 150° C. with aconstant temperature rise from 70° C. to 150° C. TABLE 5 BreakingBreaking Resins force in N stress in MPa Type of failure NRNC 2% No. 1493.1 0.251 80% adhesive NRNC 2% No. 2 503.4 0.257 70% adhesive MeanNRNC 2% 498.2 0.254 75% adhesive NRAC 2% No. 1 89.0 0.045 95% adhesiveNRAC 2% No. 2 39.1 0.020 95% adhesive Mean NRAC 2% 64.0 0.033 95%adhesive ARNC 2% No. 1 0 close to 0 100% adhesive  ARNC 2% No. 2 0 closeto 0 100% adhesive  Mean ARNC 2% 0 close to 0 100% adhesive  ARAC 2% No.1 0 close to 0 100% adhesive  ARAC 2% No. 2 28.6 0.015 100% adhesive Mean ARAC 1% 14.3 0.007 100% adhesive  Reference No. 1 372.8 0.190 90%adhesive Reference No. 2 402.2 0.205 90% adhesive Mean Reference 387.50.198 90% adhesive

[0326] Comment:

[0327] As regards the two tests on the ARNC resin and the second test onthe NRAC resin, the supports made of G₅ cast iron comprising the gasketseparate straightforwardly during the dismantling of the press, afterhaving been placed in an oven at a temperature of 130° C. It, isconsidered that the breaking force is zero and that the breaking stressis approximately equal to 0.

[0328] Analysis

[0329] The influence of the inhibitor on the antiadhesiveness of thevarnish is significant. The UV resins which do not comprise inhibitor(ARNC and ARAC) have a virtually zero breaking force and it is sometimesunnecessary to carry out the antiadhesiveness test on the supportscomprising the varnished gasket because, during the dismantling of thepress, the gasket does not have any adhesion to the supports. The ARNCand ARAC UV resins, in comparison with the reference resin (breakingforce equivalent to 387.5 N), have a greater antiadhesive property.

[0330] The inhibitor-free UV resins (ARNC and ARAC) have an adhesivefailure of 100% (90% of adhesive failure for the reference resin). Theseadhesive failures of 100% of the ARNC and ARAC UV resins prove that thelatter do not adhere to the supports made of G5 cast iron and behaveexcellently when faced with the stress-exerted by the antiadhesivenesstest.

4.2 - UV Resin of Type E

[0331] Example 4.1 is repeated, starting with the resin E described inI.1. A mixture of ARAC type having a content of photoinitiator solutionof 1% was subjected to the antiadhesiveness test.

[0332] Results:

[0333] breaking force in N: 0,

[0334] breaking stress in MPa: close to 0,

[0335] type of failure: 100% adhesive.

EXAMPLE 5 Monitoring of the Dynamic Viscosity of the UV Resins (NRNC,NRAC, ARNC and ARAC) with a 2% Content of Photoinitiator Solution

[0336] The object of this experiment is to evaluate the dynamicviscosities of each UV resin over a period of three days and to followits change, in order to assess the pot life of each resin studied.

[0337] Results: TABLE 6 Resins NRNC 2% NRAC 2% ARNC 2% ARAC 2% Dynamic340 290 305 310 viscosity 1st day (centipoise) Dynamic 360 325 330 solidviscosity crosslinked 3rd day resin (centipoise)

[0338] The inhibitor used is the same as above (Tinuvin).

EXAMPLE 6 Determination of the Rate of Polymerization of the UV Resins

[0339] The object of this example is to evaluate the rate ofpolymerization of each type of UV resin and to find out at what contentof photoinitiator it is fastest, in order to confirm the resultsobtained above and to estimate the highest degree of crosslinking. Therate of polymerization is determined using a VNC RAPRA UV device(Company Rapra Ltd).

[0340] The time at which 95% (T95) of the resin has crosslinked ismeasured. This time will subsequently be plotted on graphs.

6.1. UV Resin of Type A

[0341] The appended FIG. 1 represents the T95=f(content of 18%photoinitiator solution) curves for the resin A, the composition beingvaried as indicated below:

[0342] NRNC=UV resin of type A with 50 ppm inhibitor and photoinitiatordiluted in butyl lactate

[0343] NRAC=UV resin of type A with 50 ppm inhibitor and photoinitiatordiluted in IPA

[0344] ARNC=UV resin of type A without inhibitor and photoinitiatordiluted in butyl lactate

[0345] ARAC=UV resin of type A without inhibitor and photoinitiatordiluted in IPA

6.2. UV Resin of A, B, C. D and E type (cf. I1)

[0346] The appended FIGS. 2 to 5 represent the T95=f(content of 18%photoinitiator solution) Rapra curves for the resins A to D according to1.1 above. The solvent is IPA. No inhibitor is provided. For the resinof type I the T95 Rapra value is 0.8 minutes with a content ofphotoinitiator solution of 1%.

EXAMPLE 7 Behaviour Towards Oils of the UV Resins 7.1 UV Resin of Type A

[0347] ▪ Principle

[0348] The behaviour towards oils makes it possible to confirm theharmlessness and the stability of the resin with regard to oilsappointed for the lubrication of the engine under the physicalconditions (temperatures) and mechanical conditions laid down by thespeed of the engine. This test is essential insofar as it makes itpossible to decide whether an antiadhesive silicone resin does notdecompose and whether it fully retains its initial properties. The aimof this test is to confirm that the resin has the appropriate qualitiesin order to be subjected as little as possible to the chemical attackswith which it is confronted and to which it is exposed during theoperation of an engine.

[0349] In order to assess the behaviour towards oils, a sample of resinof predermined mass is placed in the engine oil and is subjected to atemperature of 150° C. for 72 hours. The following parameters aresubsequently examined:

[0350] the change in mass

[0351] the variation in Shore A hardness

[0352] the difference in thickness.

[0353] When all the experimental data have been collected, the loss orthe increase in mass, in thickness and in hardness are determined as apercentage (%)

[0354] A percentage close to 0%, whatever the parameter studied (mass,hardness or thickness), confirms excellent behaviour towards oils underthe conditions of simulation of an engine operating at a steady speed(150° C.).

[0355] ▪ Results:

[0356] The behaviour towards oils was carried out for UV resins of typeA (cf. I.1) without inhibitor=AR (0.5%; 1% of photoinitiator AC or NC)and with inhibitor NR (1%; 3% of photoinitiator).

[0357] NR: UV resin with 50 ppm inhibitor

[0358] AR: UV resin without inhibitor

[0359] NC: photoinitiator diluted in butyl lactate

[0360] AC: photoinitiator diluted in IPA

[0361] The photoinitiator, the inhibitor, the resin A and the referenceresin are the same as in Examples 1 to 6.

[0362] Variation in percentage of the mass of the NR and AR UV resinsbefore and after behaviour towards oils at 150° C. TABLE 7 % Shore A % Tthickness Percentages % M mass (g) hardness (mm) NRNC 1% +6.39 breakable+2.73 NRNC 3% +6.55 breakable +4.74 NRAC 1% +7.71 breakable +2.42 NRAC3% +8.65 breakable +3.11 ARNC 0.5% +4.87 −4.95 +3.59 ARNC 1% +5.20 −2.27+2.28 ARAC 0.5% +5.75 −2.12 +1.48 ARAC 1% +6.63 −2.13 +2.78 Reference+4.90 −4.77 +1.63

[0363] ▪ Analysis:

[0364] According to the values of masses collected, the reference resinand the resin of type A-ARNC 0.5% share the best behaviour towards oils.The A-NR resins have a poorer behaviour towards oils, whereas the A-ARresins have a superior behaviour towards oils. The A-NR resins have atendency to be breakable. The Shore A hardness and the thickness of theresin A and of the reference resin are not affected by the behaviourtowards oils.

7.2. UV Resin of Type E

[0365] Example 7.1 is repeated, starting with the resin E described inI.1. A mixture of type ARAC having a content of photoinitiator solutionof 1% was subjected to the test of behaviour towards oils.

[0366] ▪ Results:

[0367] % M mass (g):+6.4,

[0368] % Shore A hardness:−2.5.

EXAMPLE 8 Behaviour Towards the Cooling Liquid 8.1. UV Resin of Type A

[0369] ▪ Principle:

[0370] The test of behaviour towards the cooling liquid is comparablewith the test of behaviour towards oils. The object of this study is toconfirm the harmlessness of the UV resin on contact with the glycol orcooling liquid. The analysis and the experimental procedure of thebehaviour towards the cooling liquid are virtually analogous to those ofthe behaviour towards oils, except that the resinous and crosslinkedsamples are placed inside an oven of 100° C. for 72 hours in 100 ml. ofcooling liquid. This test makes it possible to imitate the normalconditions of operation of an engine and to observe whether there is notdecomposition of the resin by the glycol.

[0371] ▪ Results:

[0372] The behaviour towards the cooling liquid was carried out forresins of type A (Cf.I.1) without inhibitor=AR (0.5%; 1% ofphotoinitiator AC or NC) and of type A with inhibitor NR (1%; 3% ofphotoinitiator).

[0373] NR: UV resin with 50 ppm inhibitor

[0374] AR: UV resin without inhibitor

[0375] NC: photoinitiator diluted in butyl lactate

[0376] AC: photoinitiator diluted in IPA

[0377] The photoinitiator, the inhibitor, the resin A and the referenceresin are the same as in Examples 1 to 7. TABLE 8 % Shore A % Tthickness Percentages % M mass (g) hardness (mm) NRNC 1% −8.64 breakable−6.81 NRNC 3% −3.42 breakable −4.78 NRAC 1% −5.40 breakable −2.39 NRAC3% −3.36 breakable −3.36 ARNC 0.5% −1.83 −3.30 −1.52 ARNC 1% −2.38 −2.51−3.61 ARAC 0.5% −1.80 −2.85 −2.41 ARAC 1% −4.74 −6.56 −5.34 Reference−1.30 −1.15 −0.85

[0378] ▪ Analysis:

[0379] The loss in mass caused by a behaviour towards the cooling liquidis greater for the A—NR than AR resins. However, it is the referenceresin which has the best :behaviour towards the cooling liquid (%M=−1.30). The A-NR resins with 0.5% of photoinitiator have an excellentbehaviour towards the cooling liquid comparable with that of thereference resin. After behaviour towards the cooling liquid, the A—NRresins are crumbly and breakable. The thickness and the Shore A hardnessshow little variation.

8.2. UV Resin of Type E

[0380] Example 8.1 was repeated, starting from the resin E described inI.1. A mixture of type ARAC having a content of photoinitiator solutionof 1% was subjected to the test of behaviour towards the cooling liquid.

[0381] ▪ Results:

[0382] % M mass (g):−5,

[0383] % Shore A hardness:+8.

EXAMPLE 9 Determination of the Level of Crosslinking by the Level ofExtractables (Ext)

[0384] ▪ Principle:

[0385] Evaluation of the influence of a solvent on the chemicalstructure of the crosslinked silicone resin. A cylindrical resin testspecimen is placed for 72 h in the solvent, care being taken to weigh itbeforehand.

[0386] The level of extractables corresponds to the percentage of massof resin extracted by the solvent (methylcyclohexane). If this level ishigh, the mass recovered by the solvent is therefore high. This mass isdirectly related to the degree of crosslinking because the greater thelevel of extractables, the poorer the crosslinking of the resinanalysed. This is because a high level of extractables means that thesolvent more readily attacks or decomposes the resin. Conversely, a lowlevel of extractables corresponds to a consequent level of crosslinking.

[0387] initial M: mass of the resin after cross linking

[0388] swollen M: mass of the resin having absorbed solvent (72 hours inmethylcyclohexane)

[0389] ext M: mass of resin recovered by the solvent (initial M−final M)

[0390] final M: initial mass minus the mass extracted by the solvent(spell in an oven of the swollen mass at 70° C. for 24 hours)

[0391] Level of extractables:

[0392] Ext %=(initial M−final M)*100/initial M The resin A (cf. I.1),the reference resin, the inhibitor (with NR−50 ppm, without AC) and thephotoinitiator are the same as in Examples 1 to 8.

[0393] ▪ Results:

[0394] The experimental conditions are the same as in Example 8. TABLE 9Initial Swollen Final % M M Ext M M % S Ext Mc NRNC 1% 2.9110 4.43200.1460 2.7650 52.25 5.02 495.29 NRNC 3% 2.8125 4.4735 0.1005 2.712059.06 3.57 728.13 NRAC 1% 2.5855 3.9345 0.0995 2.4860 52.17 3.85 454.87NRAC 3% 2.8650 4.9560 0.2375 2.6275 72.98 8.29 788.58 ARNC 3.0115 4.10600.0955 2.9160 36.34 3.17 263.83 0.5% ARNC 1% 2.6150 3.6925 0.1100 2.505541.20 4.19 316.62 ARAC 2.8315 3.9870 0.1580 2.6735 40.81 5.58 312.080.5% ARAC 1% 2.6935 4.1585 0.1190 2.5745 54.39 4.42 485.89 Reference2.7440 3.9080 0.1160 2.6280 42.42 4.23 330.66

[0395] ▪ Analysis:

[0396] The A-AR resin (ARNC 0.5%, ARNC 1% and ARAC 0.5%, ARAC 1%),following an immersion of 72 hours in methylcyclohexane, has excellentphysical and chemical properties and qualities which allow it towithstand attack by the solvent. It has a low level of extractables.

1. Use for carrying out impregnation(s) and/or for preparing coating(s)which is (are) antiadhesive employed at the engine block/cylinder headinterface of engines and applied to sheet gaskets, in particularcylinder head gaskets, of compositions based on at least onepolyorganosiloxane (POS) crosslinkable by the cationic route and on aneffective catalytic amount of at least one initiator salt (PI), the saiduse being characterized in that: (i) the initiator salt (PI) is formedby a borate of an onium of an element from groups 15 to 17 of thePeriodic Classification [Chem. & Eng. News, Vol. 63, No. 5, 26 of Feb.4, 1985] or of an organometallic complex of an element from groups 4 to10 of the Periodic Classification (same reference), □ the cationicentity of the said borate being chosen from: 1) onium cations of theformula (I): [R ¹)_(n) −A−(R ²)_(m)]⁺  (I) in which formula: Arepresents an element from groups 15 to 17, such as I, S, Se, P or N, R¹represents a C₆-C₂₀ carbocyclic or heterocyclic aryl radical, it beingpossible for the said heterocyclic radical to comprise nitrogen orsulphur as heteroelements, R² represents R¹ or a linear or branchedC₁-C₃₀ alkyl or alkenyl radical; the said R¹ and R² radicals optionallybeing substituted by a C₁-C₂₅ alkoxy, C₁-C₂₅ alkyl, nitro, chloro,bromo, cyano carboxy, ester or mercapto group, n is an integer rangingfrom 1 to v+1, v being the valency of the element a, m is an integerranging from 0 to v−1, with n+m=v+1; 2) oxoisothiochromanium cationshaving the formula:

where the R⁶ radical represents a linear or branched C₁-C₂₀ alkylradical; 3) sulphonium cations where the cationic entity comprises: →3.1. at least one polysulphonium species of formula III.1

in which: the Ar¹ symbols, which can be identical to or different fromone another, each represent a monovalent phenyl or naphthyl radicaloptionally substituted with one or more radicals chosen from: a linearor branched C₁-C₁₂ alkyl radical, a linear or branched C₁-C₁₂ alkoxyradical, a halogen atom, an —OH group, a —COOH group, a —COO-alkyl estergroup, where the alkyl part is a linear or branched C₁-C12 residue, anda group of formula —Y⁴—Ar^(2,) where the Y⁴ and Ar² symbols have themeanings given immediately below, the Ar² symbols, which can beidentical to or different from one another or Ar¹, each represent amonovalent phenyl or naphthyl radical optionally substituted with one ormore radicals chosen from: a linear or branched C1-C₁₂ alkyl radical, alinear or branched C₁-C,₁₂ alkoxy radical, a halogen atom, an —OH group,a —COOH group or a —COO-alkyl ester group, where the alkyl part is alinear or branched C₁-C₁₂ residue, the Ar³ symbols, which can beidentical to or different from one another, each represent a divalentphenylene or naphthylene radical optionally substituted with one or moreradicals chosen from: a linear or branched C₁-C₁₂ alkyl radical, alinear or branched C₁-C₁₂ alkoxy radical, a halogen atom, an —OH group,a —COOH group or a —COO-alkyl ester group, where the alkyl part is alinear or branched C₁-C₁₂ residue, t is an integer equal to 0 or 1, withthe additional conditions according to which: + when t=0, the Y symbolis then a Y¹ monovalent radical representing the group of formula:

where the Ar¹ and Ar² symbols have the meanings given above, +when t=1:{circle over (10)} on the one hand, the Y symbol is then a divalentradical having the following meanings Y² to Y⁴: Y²: a group of formula:

where the Ar² symbol has the meanings given above, Y³: a single valencybond, Y⁴: a divalent residue chosen from:

a linear or branched C₁-C₁₂ alkylene residue and a residue of formula—Si(CH₃)₂O—, ★ on the other hand, solely in the case where the Y symbolrepresents Y³ or Y⁴, the Ar¹ and Ar² (terminal) radicals have, inaddition to the meanings given above, the possibility of being connectedto one another via the Y′ residue consisting of Y′¹, a single valencybond, or of Y′², a divalent residue chosen from the residues cited withrespect to the definition of Y⁴, which is inserted between the carbonatoms, facing each other, situated on each aromatic ring in the orthoposition with respect to the carbon atom directly bonded to the S⁺cation; → 3.2. and/or at least one monosulphonium species having asingle S⁺ cationic centre per mole of cation and comprising, in themajority of cases, species of formula:

in which Ar¹ and Ar² have the meanings given above with respect to theformula (III.1), including the possibility of connecting directlybetween them only one of the Ar¹ radicals to Ar² according to the wayindicated Above with respect to the definition of the additionalcondition in force when t=1 in the formula (II) involving the Y'residue; 4) organometallic cations of formula (IV): (L¹L²L³M)q⁺  (IV) inwhich formula: M represents a metal from group 4 to 10 chosen from iron,manganese, chromium or cobalt, L¹ represents a ligand bonded to themetal M via π electrons, which ligand is chosen from η³-alkyl,η⁵-cyclopentadienyl and η⁷-cycloheptatrienyl ligands and η⁶-aromaticcompounds chosen from optionally substituted η⁶-benzene ligands andcompounds having from 2 to 4 condensed rings, each ring being capable ofcontributing to the valency layer of the metal M via 3 to 8 π electrons,L² represents a ligand bonded to the metal M via π electrons, whichligand is chosen from η⁷-cycloheptatrienyl ligands and η⁶-aromaticcompounds chosen from optionally substituted η⁶benzene ligands andcompounds having from 2 to 4 condensed rings, each ring being capable ofcontributing to the valency layer of the metal M via 6 or 7 π electrons,L³ represents from 0 to 3 identical or different ligands bonded to themetal M via σ electrons, which ligand(s) is(are) chosen from CO and NO₂⁺; the total electronic charge q of the complex to which L¹, L² and L³and the ionic charge of the metal M contribute being positive and equalto 1 or 2; □ the anionic entity of the said borate having the formula:[BX_(a)R_(b)]⁻ in which formula: a and b are integers ranging from 0 to3 for a and from 1 to 4 for b, with a+b=4, the X symbols represent: ★ ahalogen atom with a=0 to 3, ★ an OH functional group with a=0 to 2, theR symbols are identical or different and represent: a phenyl radicalsubstituted by at least one electron-withdrawing group, such as OCF₃CF₃, NO₂ or CN, and/or by at least 2 halogen atoms, this being when thecationic entity is an onium of an element from groups 15 to 17, a phenylradical substituted by at least one electron-withdrawing element orgroup, such as a halogen atom, CF₃ OCF₃, NO₂ or CN, this being when thecationic entity is an organometallic complex of an element from groups 4to 10, an aryl radical comprising at least two aromatic nuclei, such asbiphenyl or naphthyl, which is optionally substituted by at least oneelectron-withdrawing element or group, such as a halogen atom, OCF₃,CF₃, NO₂ or CN, whatever the cationic entity; (2i) the POS comprises atleast one monomer and/or one oligomer and/or one polymer selected: fromcompounds comprising at least one (organo)functional bridging groupcrosslinkable by the cationic route (G_(f) _(p) ) with a heterocyclicnature having one or more electron-donating atoms, such as O, S, N andP, and/or from those comprising at least one ethylenically unsaturatedG_(f) _(p) group which is substituted by at least one electron-donatingatom which increases the basicity of the π system, and (3i) the G_(f)_(p) s are present in a proportion (expressed in eq per kg of POS) of atleast 0.01.
 2. Use according to claim 1, characterized in that the POSemployed exhibits G_(f) _(p) s of the epoxide and/or vinyl ether typeand is selected from the POSs which are: → a either linear orsubstantially linear and composed of units of formula (V), terminated byunits of formula (VI), → or cyclic and composed of units of formula (V):

in which formulae: the R¹ symbols are alike or different and represent:either a linear or branched C₁-C₆ alkyl radical which is optionallysubstituted, advantageously by one or more halogens, or an optionallysubstituted C₅-C₆ cycloalkyl radical, or an aryl or aralkyl radicalwhich is optionally substituted, in particular by halogens and/oralkoxys, the Z symbols are alike or different and represent: either theR¹ radical, or a G_(f) _(p) group corresponding to an epoxide or vinylether residue connected to the silicon via a divalent radical comprisingfrom 2 to 20 carbon atoms optionally comprising a heteroatom, at leastone of the Z symbols corresponding to a G_(f) _(p) group.
 3. Useaccording to claim 1 or 2, characterized in that the POS has a viscosityη (expressed in mPa.s at 25° C.) of between 200 and
 3000. 4. Useaccording to claim 1 or 2, characterized in that the POS has a viscosityη (expressed in mPa.s at 25° C.) of between a value of greater than 3000and 10,000.
 5. Use according to any one of claims 1 to 4, characterizedin that the (photo)initiator (PI) comprises a borate anionic entityselected from the following group:[B(C₆F₅)₄]⁻[B(C₆H₄CF₃)₄]⁻[B(C₆H₃(CF₃)₂)₄]⁻[(C₆F₅)₂BF₂]⁻[C₆F₅BF₃]⁻[B(C₆H₃F₂)₄]⁻,[B(C₆F₄OCF₃)₄]⁻ and their mixtures.
 6. Use according to any one ofclaims 1 to 5, characterized in that the cationic entity of the PI is ofthe onium type and is chosen from the following entities:[(Φ)₂I]⁺[C₈H₁₇—O-Φ-I-Φ]⁺[(Φ-CH₃)₂I]⁺[C₁₂H₂₅-Φ-I-Φ]⁺[(C₈H₁₇—O-Φ)₂I]⁺[(C₈H₁₇—OΦ-I-Φ)]⁺[(Φ)₃S]⁺[(Φ)₂-S-Φ-O—C₈H₁₇]⁺[(CH₃-Φ-I-ΦCH(CH₃)₂]⁺[Φ-S-Φ-S-(Φ)₂]⁺[(C₁₂H₂₅-Φ)₂I]⁺[(CH₃-Φ-I-ΦOC₂H₅]⁺7. Use according to any one of claims 1 to 5, characterized in that thecationic entity of the PI is an organometallic cation chosen from thefollowing group: (η⁵-cyclopentadienyl) (η⁶-toluene)Fe⁺(η⁵-cyclopentadienyl) (η⁶-1-methyl-naphthalene)Fe⁺ (η⁵-cyclopentadienyl)(η⁶-cumene) Fe⁺ bis (η⁶-mesitylene) Fe⁺ bis (η-benzene) Cr⁺.
 8. Useaccording to any one of claims 1 to 7, characterized in that the PI isan onium borate and/or a borate of organometallic cations chosen fromthe following group:[(Φ)₂I]⁺[B(C₆F₅)₄]⁻[(C₈H₁₇)—OΦ-I-Φ]⁺[B(C₆F₅)₄]⁻[C₁₂H₂₅-Φ-I-Φ]⁺[B(C₆F₅)₄]⁻[(C₈H₁₇—O-Φ)₂I]⁺[B(C₆F₅)₄]⁻[(C₈H₁₇)—O-Φ-I-Φ]⁺[B(C₆F₅)₄]⁻[(Φ)₃S]⁺[B(C₆F₅)₄]⁻[(Φ)₂S-Φ-O—C₈H₁₇]⁺[B(C₆F₅)₄]⁻[(C₁₂H₂₅-Φ)₂I]⁺[B(C₆F₅)₄]⁻[(Φ)₃S]⁺[B(C₆F₄OCF₃)₄]⁻[(Φ-CH₃)₂I]⁺[B(C₆F₅)₄]⁻[(Φ-CH₃)₂I]⁺[B(C₆F₄OCF₃)₄]⁻(η⁵-cyclopentadienyl)(η⁶-toluene)Fe⁺[B(C₆F₅)₄]⁻(η⁵-cyclopentadienyl)(η⁶-1-methylnaphthalene)-Fe³⁰ [B(C₆F₅)₄]⁻(η⁵-cylclopentadienyl) (η⁶ -cumene)Fe⁺[B(C₆F₅)₄]⁻.
 9. Use according toany one of claims 1 to 8, characterized in that the initiator (PI) isemployed in solution in an organic solvent chosen from proton-donatingsolvents.
 10. Use according to any one of claims 1 to 9, characterizedin that the support receiving the silicone coating obtained bycrosslinking by the cationic route is a sheet gasket, in particular acylinder head gasket, ∘ which is preimpregnated with at least onematerial for rendering leaktight formed by at least one crosslinkedpolymer ∘ and/or which is precoated with at least one layer of at leastone elastomer.
 11. Use according to any one of claims 1 to 10,characterized in that the coating obtained by crosslinking by thecationic route is mono- or multilayer and exhibits a thickness ofbetween 1 and 100 μm.
 12. Process for carrying out impregnation(s)and/or for preparing coating(s) which is (are) antiadhesive at theengine block/cylinder head interface of engines on supports composed ofsheet gaskets, in particular cylinder head gaskets, characterized inthat it consists essentially in employing a composition which iscrosslinkable under the effect of light radiation and optionally underthe effect of heat, the said composition and the support being those asdefined in any one of claims 1 to 11 relating to the use.
 13. Sheetgasket, in particular cylinder head gasket, characterized in that it isimpregnated and/or coated with a matrix obtained by crosslinking by thecationic route in accordance with the use as defined in claims 1 to 11and/or with the process according to claim
 12. 14. Silicone compositioncrosslinkable by the cationic route, characterized in that it isintended for carrying out impregnation(s) and/or for preparingcoating(s) which is (are) antiadhesive on sheet gaskets, in particularcylinder head gaskets, and in that it comprises: at least one POSpossessing G_(f) _(p) groups as defined in any one of claims 1 to 3, atleast one initiator, preferably a photoinitiator (PI), of an oniumborate type as defined in any one of claims 1 and 5 to 8, at least onesolvent of the PI as defined in claim 9, and at least one additivechosen from those generally employed in treatments targeted at renderingleaktight and antiadhesive the cylinder head/engine block interface andin particular sheet gaskets, such as, especially, cylinder head gaskets.